1. Field of the Invention
This invention relates to an apparatus for assembling a permanent magnet field motor. More particularly, the present invention relates to a technique that can effectively be applied to a motor comprising neodymium type rare earth magnets or the like.
2. Related Art Statement
Conventionally, motors comprising ferrite magnets as field magnets are prepared by arranging pieces of an unmagnetized magnet material at the stator side and magnetizing the pieces so as to turn them into field magnets after mounting the stator and the armature. However, when neodymium type or samarium type rare earth magnets are used as field magnets and the magnetization process is conducted after mounting the stator and the armature, it is difficult to realize field magnets that are magnetized to show a high magnetic flux density because the magnetizing yoke can only be arranged outside the stator after mounting the armature and hence the rare earth material cannot be sufficiently exposed to magnetic fluxes. Therefore, when rare earth magnets are used, it is necessary to employ a process of magnetizing the field magnets to make them show a high magnetic flux density firstly by magnetizing only the stator itself by means of a magnetizer and subsequently mounting the stator and the armature in order to fully exploit the potential of the rare earth magnet.
However, when such a process is employed and the stator is inserted into the armature, the latter is drawn into the former instantaneously because the field magnets are very powerful. Therefore, this process is dangerous when the armature is inserted by hand and hence it is accompanied by a problem of poor mounting performance. Furthermore, since the armature is abruptly and fiercely drawn into the stator at the time of assembling, the armature is adsorbed to the field magnets before it is inserted to the right position in the stator. In other words, it is difficult to insert the armature to the right position. If the armature is forcibly pushed into the stator, both the armature and the stator can be damaged.
Thus, when rare earth magnets are used as field magnets, an apparatus comprising dedicated jigs needs to be employed for the purpose of mounting the armature to the stator. For example, Japanese Patent Application Laid-Open Publication No. 2001-251817 discloses a motor assembling apparatus adapted to hold the armature and mount the stator to the outside of the armature. The invention involves the use of a jig for holding one of the opposite ends of the armature, an armature holder for holding the other end of the armature and a stator holder for holding the stator outside the armature, which stator holder is movable in the direction of the central axis. According to the invention, the armature holder is made to hold the other end of the armature, while the stator holder is being moved, and the stator is mounted outside the armature with a predetermined gap separating them. With this arrangement, the stator is prevented from being adsorbed by the armature so that the armature and the stator can be mounted smoothly and easily so as to make them show a desired positional relationship when rare earth magnets are used as field magnets.
If such an apparatus is used, the operation of magnetizing the field magnets and that of mounting the armature and the stator are conducted independently. More specifically, the stator is put on a magnetizer to magnetize the field magnets and subsequently the magnetized stator is put on an assembling apparatus of the above described type to mount it to the right position relative to the armature. However, when rare earth magnets are used as field magnets, they can adsorb dust particles and other debris so that foreign objects can enter the inside of the stator between the operation of magnetizing the field magnets and that of mounting the armature and the stator. Thus, the armature needs to be mounted to the right position relative to the magnetized stator immediately after the magnetizing operation. This means that it is not feasible to provide a large stock of prepared stators. In other words, the operation of magnetizing the stator and that of mounting the armature and the stator need to be conducted almost at the same time at the cost of efficiency of operation.
Additionally, if a step of using an assembling apparatus dedicated to mounting the armature and the stator as described above is put into the process, both the capital investment and the number of assembling steps increase to raise the overall manufacturing cost.
Therefore, it is the object of the present invention to provide a motor assembling apparatus that has a simple structure and can perform both the operation of magnetizing the stator field magnets and that of mounting the armature to the stator continuously on the apparatus to improve the efficiency of operation and prevent foreign objects from entering the stator.
According to the invention, the above object is achieved by providing a motor assembling apparatus for assembling a motor having a cylindrical stator with permanent magnets rigidly adhering to the inner peripheral surface thereof and an armature rotatably arranged in the stator, the apparatus comprising: a magnetizer having an outer magnetizing coil to be arranged outside the stator and an inner magnetizing coil to be arranged inside the stator; a stator support for supporting a lower end part of the stator, the stator support being arranged so as to be vertically movable between the outer magnetizing coil and the inner magnetizing coil along the central axial line of the stator; and an armature holder for holding the armature at one of the opposite ends thereof, the armature holder being arranged above the magnetizer, the stator support being adapted to be fitted to the outside of the armature holder; the stator having the permanent magnets magnetized by the magnetizer being fitted to the outside of the armature held on the armature holder by means of the stator support.
Thus, according to the invention, since the magnetized stator is immediately fitted to the armature held on the armature holder by way of a sliding movement of the stator support, the opportunity for foreign objects to enter the stator is minimized so as to improve the reliability of the manufactured product. Additionally, since the magnetizing step and the mounting step are conducted continuously in a same apparatus, the efficiency of operation is improved and the number of assembling steps is reduced.
A stator keeping jig may be additionally arranged above the stator support in a motor assembling apparatus according to the invention in such a way that it abuts an upper end part of the stator mounted on the stator support and is adapted to be vertically movable, while pinching the stator between itself and the stator support. With this arrangement, the stator can be pinched between the stator keeping jig and the stator support to stabilize the behavior of the stator and make it possible to reliably mount the armature and the stator.
The stator may be provided with a cylindrical yoke, permanent magnets rigidly adhering to the inner peripheral surface of the yoke and a magnet cover arranged in the inside of the permanent magnets for covering the inner surfaces of the permanent magnets. With this arrangement, since the permanent magnets are covered by the magnet cover, the armature is prevented from directly touching the permanent magnets and the permanent magnets are prevented from being damaged to produce cracks and/or notches when the stator is fitted to the armature.
On the other hand, rare earth magnets may be used as the permanent magnets in the motor assembling apparatus according to the invention. Then, although powerful rare earth magnets can adsorb dust particles and other debris, the opportunity for foreign objects to enter the stator is minimized so as to improve the reliability of the manufactured product because the armature is immediately fitted to the magnetized stator. Additionally, since the magnetizing step and the mounting step are conducted continuously in a same apparatus, the otherwise dangerous operation is automated to improve both the safety and the efficiency of operation and the number of assembling steps is reduced. Furthermore, it is possible to provide an armature holder having no functional feature of aligning the armature with the stator to allow it to show a simple structure that is adapted to simply hold one of the opposite ends of the armature.
The above described object and other objects of the present invention will become apparent along with novel features of the invention more fully from the description of the specification given below in conjunction with the accompanying drawings.